This invention relates to new isocyanatobenzylcyclohexyl isocyanates which are mono-substituted on the aromatic ring, optionally in the form of isomeric mixtures. The present invention also relates to a process for the production of such isocyanates by the phosgenation of the underlying diamines or diamine mixtures.
Asymmetric diisocyanates having an aromatically bound and a cycloaliphatically bound isocyanate group would be eminently suitable for the production of polyurethanes by the prepolymer process due to the wide difference in reactivity between these isocyanate groups. The more highly reactive, aromatically bound isocyanate group would be the first to react, forming the isocyanate prepolymer, which would then react in a second stage to form the high molecular weight polyurethane.
Such asymmetric diisocyanates would also be suitable for the preparation of modified isocyanates, as for example, uretdione diisocyanates. The more highly reactive isocyanate group would react in the first reaction stage and undergo dimerization to form a diisocyanate containing uretdione groups. This modified diisocyanate could then be reacted with compounds containing isocyanate reactive groups.
U.S. Pat. No. 3,663,514 describes one such diisocyanate, namely 4-(4-isocyanatobenzyl)cyclohexyl isocyanate. This diisocyanate has not been used to any great extent because the diamine from which this diisocyanate is produced is only obtainable in yields of less than 35% of theoretical by asymmetric hydrogenation on the nucleus. Consequently, the pure asymmetric diisocyanate can only be obtained after elaborate purification.